1. Field of the Invention
The present invention relates to an exhaust emission purifying apparatus for purifying an exhaust gas from an engine by eliminating nitrogen oxides (NOx) in the exhaust gas by reduction using a reducing agent, and in particular, to an exhaust emission purifying apparatus for an engine, that is provided with a swirling flow generating means disposed in an exhaust passage for generating a swirling flow of the exhaust gas in order to increase efficiency in purifying of the exhaust gas.
2. Description of the Related Art
As a catalytic purifying system of eliminating NOx contained in the exhaust gas of an engine, there has conventionally been proposed an exhaust emission purifying apparatus. In such a conventional exhaust emission purifying apparatus, a NOx reduction catalytic converter is disposed in an exhaust passage of the engine, and a reducing agent such as a urea aqueous solution or the like, is injected from an injection nozzle disposed on an exhaust upstream side of the NOx reduction catalytic converter, so that the exhaust gas and the reducing agent are mixed with each other, and NOx in the exhaust gas and the reducing agent are subjected to the catalytic reduction-reaction to each other in the NOx reduction catalytic converter, so that NOx is purified into harmless components (refer to Japanese Unexamined Patent Publication No. 2001-20724).
However, in the above conventional exhaust emission purifying apparatus, there might be a possibility that the mixing of the reducing agent with the exhaust gas is insufficient, when injection of the reducing agent is carried out at a position located on the exhaust upstream side of the NOx reduction catalytic converter. Then, if the mixing of the reducing agent with the exhaust gas is insufficient as described above, the reducing agent non-uniformly flows into the NOx reduction catalytic converter, and as a result, there might be a possibility that the exhaust gas purification efficiency is lowered.